Polydopamine-assisted in-situ formation of dense MOF layer on polyolefin separator for synergistic enhancement of lithium-sulfur battery

The separator is of great significance to alleviate the shuttle effect and dendrite growth of lithium-sulfur batteries. However, most of the current commercial separators cannot meet these requirements well. In this work, a dense metal-organic-framework (MOF) modification layer is in-situ prepared by the assistant of polydopamine on the polypropylene separators. Due to the unique structure and synergistic effect of polydopamine (PDA) and zeolitic imidazolate framework-8 (ZIF-8), the functional separator can not only trap the polysulfides effectively but also promote the transport of lithium ions. As a result, the battery assembled with the functional separator exhibits excellent cycle stability. The capacity remains 711 mAh·g−1 after 500 cycles at 2 C, and the capacity decay rate is as low as 0.013% per cycle. The symmetrical battery is cycled for 1,000 h at 2 mA·cm2 (2 mAh·cm−2) with the plating/stripping overpotential of 20 mV. At the same time, the modification separator shows a higher lithium ion transference number (0.88), better thermal stability and electrolyte wettability than the unmodified separator.